matchers.js

const isNumber = require('lodash/isNumber');
const isString = require('lodash/isString');

expect.extend({
    toBeArray(received) {
        return {
            pass: Array.isArray(received),
            message: () => `Expected ${received} to be array`
        };
    },

    toBeArrayOfStrings(received) {
        let pass = Array.isArray(received);

        if (pass) {
            received.forEach(x => {
                if (!isString(x)) pass = false;
            });
        }

        return {
            pass,
            message: () => `Expected ${received} to be array`
        };
    },

    toBeString(received) {
        return {
            pass: isString(received),
            message: () => `Expected ${received} to be string`
        };
    },

    toBeNumber(received) {
        return {
            pass: isNumber(received),
            message: () => `Expected ${received} to be number`
        };
    }
});

matchers.test.js

test('matchers', () => {
    expect([]).toBeArrayOfStrings();
    expect(['1', '2', '3']).toBeArrayOfStrings();

    expect({}).not.toBeArrayOfStrings();

    expect([1, 2]).not.toBeArrayOfStrings();
    expect([1, '2']).not.toBeArrayOfStrings();
    expect(['1', 2]).not.toBeArrayOfStrings();

    expect({}).not.toBeArrayOfStrings();
    expect('').not.toBeArrayOfStrings();
});